Fix dashboard link to display all of Your Posts

Quick link on dashboard to show all your posts was linking to the following URL:

    http://localhost:3000/admin/content?search=search[user_id]%3D1

"search" is expected to be a hash, not a normal query string key. Link needs instead to send:

    http://localhost:3000/admin/content?search[user_id]=1

Now matches the expected search filter calls also used in "Manage articles" admin section.

Fixes #110